The invention relates to a suspension actuator for positioning a movably mounted component of a vehicle suspension, with the actuator comprising a first actuator component for connecting to the movably mounted component and a second actuator component for connecting to a fixed suspension component, wherein both actuator components can be adjusted relative to each other in the axial direction by a ball-type screw drive comprising a threaded spindle and a nut running on this spindle, wherein either the nut can be driven by a drive motor for the axial adjustment of the threaded spindle or the spindle can be driven by the drive motor for the axial adjustment of the nut.
Such a suspension actuator is used in suspensions of vehicles, for example, on a wheel suspension of a vehicle wheel. By use of the suspension actuator that can be driven independently, a desired adjustment of the suspension-side, movably mounted component, such as, for example, of a wheel carrier or the like, is possible. A suspension actuator suitable for this purpose, as is known, for example, from DE 10 2005 023 250 A1, has available two actuator components, wherein a first actuator component is connected to the suspension component to be adjusted and a second actuator component is connected to a fixed suspension component, thus it is supported there on the vehicle body. Both actuator components could be adjusted relative to each other in the axial direction, with a ball-type screw drive being used for this purpose. This drive comprises a threaded spindle by which both actuator components are connected, as well as a nut running on this spindle, with the nut running on the spindle via balls located in-between. For the axial adjustment of the spindle and thus for moving the actuator components away from or toward each other for the desired suspension adjustment, a drive motor is used that rotates the fixed nut, which leads to the axial movement of the spindle relative to the fixed nut. A different construction provides a fixed spindle rotationally driven by the drive motor, while the nut that is connected to the suspension part for positioning is moved axially. Such suspension actuators—typically an independent suspension actuator that can be driven separately is allocated to each wheel—take over safety-relevant tasks, which is why, in principle, there is the requirement that the linked suspension components do not carry out undesired positioning movements, for example, when there is the loss of an actuator, but instead are held in the last set position. Likewise it must be guaranteed that external forces that are introduced in the reverse direction into the actuator via the suspension are absorbed reliably, without the actuator carrying out undesired positioning movements due to these external forces.
For this purpose, in the suspension actuator according to DE 10 2005 023 250 A1, a locking mechanism in the form of a mechanical ramp catch is provided that has a switchable construction. This locking mechanism blocks the driven part, that is, the nut, when the driving force of the actuator is less than an external force acting on the nut, wherein this force is applied either by the drive motor or is 0 for an adjustment that has not yet been performed. For example, if the suspension actuator described there is used for active adjustment of the wheel camber of a wheel of a motor vehicle, for example, shocks introduced into the wheel from the outside are forwarded only up to the driven part, that is, the nut of the actuator. An introduction of these shock forces into the actuator up to the motor is ruled out, because the driven part, that is, the nut, is blocked by the locking mechanism. The shock forces are introduced into the fixed suspension itself by the locking mechanism. The locking mechanism itself is constructed in the known suspension actuator as a clamping-roller locking mechanism and comprises a clamping ring provided with clamping ramps and a hollow-cylindrical part with a cylindrical clamping track that forms, together with the clamping ramp part, the clamping gap in which the clamping rollers are arranged that can be switched into and out of clamping engagement with the clamping ramps. The clamping rollers themselves are constantly ready for clamping, for which purpose they are biased with springs.
Such a clamping-roller locking mechanism could indeed realize the desired actuator locking that satisfies the requirements named above. However, such clamping locking with clamping ramps knows, in principle, only two positions, namely the locked position or the unlocked position. From this situation, problems can result when the spindle is to be adjusted in the loading direction, i.e., an external force is applied that acts in the positioning direction. This leads to so-called “locking jerking movements.” These are generated because the load constantly overtakes the drive, i.e., the clamping rollers are constantly brought into the clamping position by the external load. When the drive motor has somewhat “caught up” to the load again, the motor opens the clamping locking mechanism again, whereupon the load overtakes the drive again, resulting again in the locking of the locking mechanism, and so on. This, however, is disadvantageous or not permissible in many applications.